聚球藻Synechococcus sp.PCC7942高CO_2需求突变株的筛选及其超微结构观察(英文)

以单细胞蓝藻聚球藻Synechococcussp.PCC7942为材料,利用甲基磺酸乙酯(EMS)进行化学诱变获得了一个高CO2 需求突变株。它能在 4%CO2 下生长而不能在空气中生长。对突变株的初检表明:其回复突变率约为 10 -7。该突变株从高CO2 条件下转到空气中后,细胞在 2～ 3d内逐渐趋于死亡;其光合作用对外源无机碳的依赖性高于野生型细胞,碳酸酐酶活性也低于野生型细胞。在超微结构水平,突变株细胞内出现了不同类型的异常羧体:有的为棒状;有的为不规则状;有的为 空羧体",而且,类囊体周围糖原颗

ApcD is necessary for efficient energy transfer from phycobilisomes to photosystem I and helps to prevent photoinhibition in the cyanobacterium Synechococcus sp PCC 7002

Phyrobilisomes (PBS) are the major light-harvesting, protein-pigment complexes in cyanobacteria and red algae. PBS absorb and transfer light energy to photosystem (PS) II as well as PS I, and the distribution of light energy from PBS to the two photosystems is regulated by light conditions through a mechanism known as state transitions. In this study the quantum efficiency of excitation energy transfer from PBS to PS I in the cyanobacterium Synechococcus sp. PCC 7002 was determined, and the results showed that energy transfer from PBS to PS I is extremely efficient. The results further demonstrated that energy transfer from PBS to PS I occurred directly and that efficient energy transfer was dependent upon the allophycocyanin-B alpha subunit, ApcD. In the absence of ApcD, cells were unable to perform state transitions and were trapped in state 1. Action spectra showed that light energy transfer from PBS to PS I was severely impaired in the absence of ApcD. An apcD mutant grew more slowly than the wild type in light preferentially absorbed by phyrobiliproteins and was more sensitive to high light intensity. On the other hand, a mutant lacking ApcF, which is required for efficient energy transfer from PBS to PS II, showed greater resistance to high light treatment. Therefore, state transitions in cyanobacteria have two roles: (1) they regulate light energy distribution between the two photosystems; and (2) they help to protect cells from the effects of light energy excess at high light intensities. (C) 2009 Elsevier B.V. All rights reserved.

Growth and antioxidant system of the cyanobacterium Synechococcus elongatus in response to microcystin-RR

Microcystins, one type of the cyanobacterial toxins, show a broad range of hazardous effects on other organisms. Most of the researches on the toxic effects of microcystins have involved in animals and higher plants. Little work, however, has been done on evaluating the mechanisms of microcystin toxicity on algae. In this study, the toxicological effects of microcystin-RR (MC-RR) on the cyanobacterium Synechococcus elongatus were investigated. For this purpose, six physio-biochemical parameters (cell optical density, reactive oxygen species (ROS), malondialdehyde (MDA), glutathione (GSH), glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST)) were tested in algal cells when exposed to 100 mug(-1) microcystin-RR. The results showed that the growth of Synechococcus elongatus ( expressed as optical density) was significantly inhibited compared with the control. At the same time, the treated algae exhibited a pronounced increase in production of ROS and MDA after 6 days exposure to microcystin-RR. Signi. cant changes in GSH levels and GSH-Px, GSH activities were also detected in algal cells, with higher values being observed in the toxin treated algae after 6 days exposure. GST activities in the treated algae exhibited a decline after exposure and rapid augmentation on day 3, thereafter, they kept at a high level when compared to the control group. GSH contents and GSH-Px activities were also significantly raised in the toxin-treated algae cells from day 3, but they showed a sharp decrease on day 4, which was the onward of cell proliferation. These results suggested that oxidative stress manifested by elevated ROS levels and MDA contents might be responsible for the toxicity of microcystin to Synechococcus elongatus and the algal cells could improve their antioxidant ability through the enhancement of enzymatic and non-enzymatic preventive substances.

Physiological and biochemical microcystin-RR toxicity to the Synechococcus elongatus

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 mug (.) L-1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F-v/F-m) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. (C) 2004 Wiley Periodicals, Inc.

Selection and ultrastructural observation of a high-CO2-requiring mutant of cyanobacterium Synechococcus sp PCC7942

A high-CO2-requiring mutant of Synechococcus sp. PCC7942 las been isolated after chemical mutagenesis of ethyl methane sulphonate (EMS). It was able to grow at 4% CO2, but not under ambient CO2. The initial screening of the mutant showed that the genetic reversion rate was about 10(-7) and death occurred 2 -3 days after being transferred from 4% CO2 to the ambient air. Its photosynthetic dependence on external dissolved inorganic carbon was higher than that of the wild type cells, but its carbonic anhydrase activity was comparatively low. In the ultrastructural level, various types of aberrant carboxysomes appeared in the mutant cells: rod-shaped carboxysomes, irregular carboxysomes and the "empty-inclusion carboxysomes" with increasing number of glycogen granules surrounding the thylakoids. All these alterations indicated that the mutant was defective in utilizing the external CO2. The induction of carboxysomes by lower levels of CO2 and the biogenesis of carboxysomes are herein discussed.

Evidence for positive selection in phycoerythrin genes of red algae and cyanobacteria Prochlorococcus and Synechococcus

Because of the shortage of phycoerythrin (PE) gene sequences from rhodophytes, peBA encoding beta- and alpha-subunits of PE from three species of red algae (Ceramium boydenn, Halymenia sinensis, and Plocamium telfariae) were cloned and sequenced. Different selection forces have affected the evolution of PE lineages. 8.9 % of the codons were subject to positive selection within the PE lineages (excluding high-irradiance adapted Prochlorococcus). More than 40 % of the sites may be under positive selection, and nearly 20 % sites are weakly constraint sites in high-irradiance adapted Prochlorococcus. Sites most likely undergoing positive selection were found in the chromophore binding domains, suggesting that these sites have played important roles in environmental adaptation during PE diversification. Moreover, the heterogeneous distribution of positively selected sites along the PE gene was revealed from the comparison of low-irradiance adapted Prochlorococcus and marine Synechococcus, which firmly suggests that evolutionary patterns of PEs in these two lineages are significantly different.

海洋聚球蓝细菌（Synechococcus���的纯化鉴定及生理和生态分布特征

利用流式细胞仪分析了聚球蓝细菌在胶州湾的时空分布和营养盐的影响, 并对聚球蓝细菌亚群分化及其影响因子做了进一步探索。分离获得六株海洋聚球蓝细菌，分别定名为IOCAS0401、IOCAS0402、IOCAS0403、IOCAS0404、IOCAS0405、IOCAS0406。对其中两株（IOCAS0401、IOCAS0402）进行鉴定，并进一步研究了其生理生态特征。有三株菌（IOCAS0403、IOCAS0404、IOCAS0405）具有异养生长能力，选取其中两株（IOCAS0403、IOCAS0405）构建了遗传操作系统。具体内容摘要如下： 1、聚球蓝细菌在胶州湾的时空分布和营养盐的影响 胶州湾近一年的微微型浮游植物群落分析表明，聚球蓝细菌逐月的最高丰度中心有从湾外→湾口→湾内，再由湾内→湾口→湾外的变化趋势。在月变化中，聚球蓝细菌9月丰度最大，平均丰度为4.87×103 cells/ml，1-4月丰度很低，其中3月平均丰度最低为66 cells/ml。选取D5站的0 m和30 m作为表层和深层，对微微型浮游植物和营养盐的研究表明，在9、10月，N/P主要在10-30之间，聚球蓝细菌占优势51.6%（9月），98.5％（10月），其它月份大多数N/P<10或者>30，尤其以8月和11月最为显著，而这两个月也恰恰是超微真核浮游植物占优势92.1％（8月），84.8％（11月）。流式细胞仪数据表明，夏末和秋季部分站位会出现聚球蓝细菌的两个亚群，并且当N/P在33左右时可能会出现两个亚群分化，经过对N源的分析后发现，产生亚群分化时NO3-N/PO4-P在14左右。 2、 所分离到的六株聚球蓝细菌的吸收光谱表明，胶州湾的聚球蓝细菌色素种类十分丰富，基本都含有叶绿素a和藻红蛋白（PE），同时也有含藻蓝蛋白（PC）的种群。研究中发现有三株菌具有兼性异养生长能力，当有光照的时候，合成色素，自养生长进行产氧光合作用，没有光照时，色素逐渐消失，启动异养生长的代谢过程。 3、 利用流式细胞仪分析黄海近海水样中聚球蓝细菌种群组成，发现主要有不同藻红蛋白含量的两个类群组成，流式细胞仪分选后，用SN培养基培养纯化得到两个亚群优势种聚球蓝细菌IOCAS0401和IOCAS0402。荧光显微镜下镜检，两株菌在蓝色激发光（450-490 nm）下发桔红色荧光，并且IOCAS0401的荧光较IOCAS0402强。扫描电镜观察发现IOCAS0401呈椭圆形，长轴大约1.2 μm左右；IOCAS0402近似球形，直径约有0.6 μm左右。吸收光谱的检测表明，两者都有叶绿素a和藻红蛋白的特征吸收峰。其中IOCAS0401有藻尿胆素（PUB）和藻红胆素（PEB）吸收锋，而IOCAS0402只有PEB的吸收峰，两者均无藻蓝蛋白（PC）吸收锋。通过16S rDNA测序分析，结果表明两株菌都位于MC-A中的clade II类群，与从日本海域分离获得的MBIC10224菌株有较高的亲缘关系，虽然这三株菌都归为clade II，但单独成一分支，表明它们带有明显的西太平洋特色。 4、 选取其中两株IOCAS0403和IOCAS0405构建遗传系统，抗生素图谱表明，IOCAS0403对四环素有抗性，自然转化结果显示，IOCAS0403不能自然转化，IOCAS0405具有自然转化能力，同时两者都不能进行接合转移。

Determinação da estrutura e estudo da função da metalotioneína de Synechococcus com ferramentas da bioinformática.

Este trabalho abordou a análise estrutural das MTs a fim de se modelar esta proteína e com isso compreender melhor o funcionamento da mesma. O conhecimento da cianobactéria e uma completa análise da MT poderia ser muito útil em um estudo de utilização desta na técnica da biorremediação para remover metais pesados do solo e da água decorrentes das praticas agrícolas atuais.